It is planned to study in a controlled fashion, the effect of pH variation, topically both on the parietal cells and on antral gastrin release. Calcium and magnesium ion, reportedly having some opposite physiological effects, will also be investigated. In this manner, it's hoped to learn more about pH dependent antral gastrin inhibition and stimulation as separated from the effect of the specific ions themselves. Similarly, direct topical effects on the parietal cells should be differentiated from those which work via gastrin release. The mechanism of calcium ion induced release of polypeptides from endocrine cells will be defined by establishing the role of calcium ions in the function of these cells of the membrane, cytosol, and mitochondrial levels. An attempt will be made to experimentally differentiate, as has been done in regard to acid secretion, the effect of hypercalcemia from that of increased levels of parathormone on antral G-cell mass. The effect of calcitonin, as well, will be studied. By studying the G-cell population in various clinical situations, some insight into its importance in the pathophysiology of stress ulceration and the effect of treatment modalities commonly employed is expected. BIBLIOGRAPHIC REFERENCES: Levine, B., Greenburg, A. G., McLaughlin, M., Peskin, G. W., Saik, R. P.: Antral gastrin regulation. J. Surg Res. 20: 509, 1976. Saik, R. P., Greenburg, A. G., Peskin, G. W., The hazard of cholecystostomy in acute cholangitis. JAMA. 235:2412, 1976.